Apparatus for casting directionally solidified articles

ABSTRACT

Casting apparatus for the production of directionally solidified castings comprises first, second and third chambers and valves between the first and second and second and third chambers. The first chamber holds a charge melting and pouring arrangement. The second comprises a casting chamber and the third is a withdrawal chamber so that the casting may be withdrawn in a controlled fashion from the second chamber to produce the required directional solidification.

United States Patent 11 1 Higginbotham et a1.

1 Nov. 5, 1974 22 Filed:

1 APPARATUS FOR CASTING DIRECTIONALLY SOLIDIFIED ARTICLES [75]Inventors: Gordon John Spencer Higginbotham, Darley Abbey; KennethCuckson, Allestree, both of England [73] Assignee: Rolls-Royce (1971)Limited,

London, England Nov. 30, 1972 [21] App]. No.: 310,966

[30] Foreign Application Priority Data Dec. 4, 1971 Great Britain56395/71 [52] U.S. Cl 164/258, 164/130, 164/136, 164/122 [51] Int. ClB22d 27/16 [58] Field of Search 164/80, 130, 136, 258, 164/65 [56]References Cited UNITED STATES PATENTS 2.825945 3/1958 Ulrech et al.164/258 3,008,855 11/1961 Swenson 148/32 3,484,840 12 1969 Spoth et61... 164 80 ux 3,532,155 10 1970 Kane et al 164 65 x FOREIGN PATENTS ORAPPLICATIONS 547,954 10/1957 Canada 164/258 2331751 5/1964 Austria164/258 Primary Examiner-Andrew R. Juhasz Assistant ExaminerJohn E.Roethel Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACTCasting apparatus for the production of directionally solidifiedcastings comprises first, second and third chambers and valves betweenthe first and second and second and third chambers. The first chamberholds a charge melting and pouring arrangement. The second comprises acasting chamber and the third is a withdrawal chamber so that thecasting maybe withdrawn in a controlled fashion from the second chamberto produce the required directional solidification.

9 Claims, 2 Drawing Figures APPARATUS FOR CASTING DIRECTIONALLYSOLIDIFIED ARTICLES This invention relates to apparatus for casting andis particularly concerned with apparatus for carrying out the processknown as directional solidification.

The term directional solidification refers to a process of casting inwhich the heat flow from the casting during solidification is controlledso that the grains within the final casting extend at leastsubstantially unidirectionally. It has been found that this process canproduce castings which have improved properties, and particularly in theproduction of such articles as turbine blades for gas turbine engines,it is possible by the use of directional solidification to produce anarticle whose properties may be more reliably specified than when usingconventional casting.

The present invention relates to apparatus in which directionalsolidification may be carried out in a simple fashion and which lendsitself to automation.

According to the present invention apparatus for casting comprises firstsecond and third adjacent chambers each of which may be sealed andevacuated, the first and second valve means dividing said first fromsaid second chamber and said second from said third chamberrespectively, and a charge melting arrangement in said first chamberadapted to melt metal and discharge it through said first valve meansinto said second chamber, a mould heating furnace in the second chamberadapted to heat a mould which receives said molten metal, and a movablechill support adapted to carry a chill and a mould between said secondand said third chambers whereby the mould may be introduced into thefurnace and removed when charged from the second to the third chamber sothat a directional grain structure may be formed in the casting.

Preferably said first, second and third chambers are mounted on abovethe other with the first chamber being the topmost.

Said charge melting arrangement may also comprise an automatic bottompouring arrangement.

There may also be charging means for the bottom pouring arrangementwhich comprises a flange member which carries a crucible which holds thenew charge, the flange sealing a charging hole in the first chamber whenthe crucible is in position in the bottom pouring arrangement.

Preferably there are separate ducts connected to said first, second andthird chambers for evacuation of these chambers; in this case the valvesmay be so sequenced as to maintain at all times during the operation avacuum within the second chamber.

We prefer that the charged mould should be introduced and withdrawn fromthe second chamber at a non-constant rate.

There may be a pair of said charge holding crucibles and flanges and apair of said third chambers and chill supports which may be alternatelymovedinto position with respect to the first and second chambers, thusenabling loading and unloading of the crucible and mould respectively onthe crucible and third chamber which are not adjacent the first andsecond chambers.

In a combined production facility it would be possible to use a singlevacuum pumping unit (which may comprise a number of pumps) and a singlepower supply for the bottom pouring equipment; with suitable switchingand sequencing means it is possible for such a single unit to service aplurality of the chamber combinations. Alternatively a single powersupply could be used together with a number of vacuum units eachservicing a number of chambers.

The invention will now be particularly described merely by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a sectional view of apparatus for casting in accordance withthe present invention, and

FIG. 2 is a diagrammatic plan view of the lay-out of a productioncasting unit using the apparatus of the invention.

In FIG. 1 there is shown casting apparatus comprising a first meltingchamber 10, which is mounted on top of a second furnace chamber 11 andwhich in the condition shown in FIG. 1 is on top of a third withdrawalchamber 12. The melting chamber is separated from the furnace chamber byan upper gate valve 13 while the furnace chamber is separated from thewithdrawal chamber by a second lower gate valve 14. It should be notedthat it may be preferable to use a different form of valve, e.g. a liftand swing valve, and that in order to prevent damage to the valve sealsand to provide a more rapid rate of change of temperature between thefurnace chamber and the withdrawal chamber it may be desirable to watercool the valve itself. The upper gate valve is operated by a ram 15while the lower gate valve is operated by a ram 16. All the chambers arearranged to be evacuated by way of ducts 17, 18 and 19 respectivelywhich are connected to a vacuum pump when evacuation is necessary; ducts17 and 19 are connected to the pump by way of a single valve 20 whileduct 18 has a separate valve 21. A further valve 22 is also provided bywhich ducts 17 and 19 may be vented to atmosphere.

Within the chamber 10 there is positioned as induction coil 23 whichforms part of an automatic bottom pouring arrangement. The coil issupplied with electricity through bus bars 24 and 25 and is cooled withwater through pipes 26 and 27. The electricity supply to the coil iscontrolled by an automatic sequencing unit which is not shown in FIG. 1.

In the condition shown in FIG. 1 a crucible 28 is mounted in positionwithin the induction coil 23. The crucible 28 carries a charge of metal29 and is suspended from a flange 30. The bottom of the crucible may besupported on a location plate (not shown) above the valve 13. The flange30 is moved vertically by a ram 31, and seals the charging hole 32 inthe top surface of the chamber 10.

The gate valve 13 is shown in the open position and hence allows freepassage of molten metal from the crucible 28 into the furnace chamber11. Within this chamber there is a mould heating furnace (32)electrically heated either by a resistance heater in the form of eithera single element or by a plurality of elements,

which is the preferred method, or alternatively an induction heatedsusceptor may be used. The heater surrounds a central area within whicha mould 33 is shown carried on a water cooled chill 34 which is in turnsupported on a spindle 35 which is carried in bushes 36 and 37 which areformed-in support arms 38 and 39.

Water cooling for the chill 34 is effected by ducts which extend withinthe spindle 35 from inlet and outlet ports 41 and 42 at its extremity.

The arm 38 carries the major portion of the withdrawal chamber 12 whichcomprises a cylindrical chamber mounted co-axially on the spindle 35 andsealed to it just above the bush 36. The walls of the cylindricalchamber are cooled by water which flows through ducts 100 in the walls,the cooling water being supplied from flexible pipes (not shown). Theopen end of the chamber 12 seals against the stationary plate 43 whichis carried from the lower portion of the chamber 11 and which enclosesthat part of the chamber 12 which provides space for the gate valve 16.This valve is shown as being open and consequently allows the chill 34and hence the mould 33 to be withdrawn vertically from chamber 11,vertical movement of the spindle 35 being permitted by its slidingwithin the bushes 36 and 37.

To effect vertical movement of the spindle 35, a ram 44 is mounted tomove a plate 45 in a vertical direction. The plate 45 engages in theslot of a flange bush 46 which is fixed to the spindle 35. Hence,vertical movement of the plate 45 will cause vertical movement of thespindle 35. To control the rate at which this vertical movement occurs,a cam 47 is also mounted from the plate 45, and the cam engages with afeedback device 48 which controls the pressure of fluid supplied to theram 44, thus providing a predetermined rate of rise and fall of thespindle 35. Microswitches 49 and 50 cooperate with end faces of the cam47 to limit the vertical travel of the spindle 35 in the upward anddownward direction respectively.

The hydraulic ram 44 may be replaced by other devices, thus a leadscrewcould be used to raise and lower the spindle 35, the leadscrew beingrotated by a hydraulic or electric variable speed motor. The leadscrewwould enable easier control of the vertical position of the spindle.

To provide a simple charging and mould removing arrangement theapparatus is provided with two charge crucible support arrangements andtwo mould support arrangements. Thus the ram 31 is supported by an arm51 from the upper end of the indexing spindle 40, the arm 51 extendingthe same distance the other side of the spindle 40 to support a ram 52exactly similar to the ram 31 and which carries a flange 53 similar tothe flange 30. The flange 53 is shown carrying a fresh crucible 54 whichcontains a fresh charge of metal 55. In a similar fashion the arms 38and 39 extend on the other side of the spindle 40 and carry a furthersupporting spindle 56 which is similar to the spindle 35 and whichcarries a further withdrawal chamber 57 within which are a chill 58 andmould 59.

It would be appreciated that the crucible 54 and the mould 59 may easilybe replaced while the spindle 56 is in the position shown and clear ofthe first and second chambers and 11.

To enable either of the chambers 12 and 57 to be engaged with the lowersurface of the plate 43, the indexing spindle 40 is mounted on a ramunit 60 which comprises an indexing ram 61 which rotates the spindle soas to bring either the flange 30 and chamber 12 or the flange 53 of thechamber 57 into position with respect to the first and second chambers10 and 11. A second cylinder 62 raises or lowers the spindle 40 so as toengage the upper surface of the chamber 12 or 57 with the remainder ofthe apparatus.

FIG. 2 shows how a number of these units may be layed out to takeadvantage of a single vacuum unit and induction coil supply unit,although depending on the pipework etc. required it may be more economicto use a vacuum unit for a smaller plurality of casting units. It willbe understood that each vacuum will comprise a plurality of pumps eachoperating over a different pressure range. It will be seen that aplurality of separate units 70, 71, 72 etc. are mounted in a ring aboutin this case a single central vacuum unit and induction coil supply unit81. A sequencing unit 83 is is provided which operates the variousvalves of each unit in turn and which actuates the vacuum unit and theinduction coil supply.

Operation of the system is as follows:

In the condition shown in FIG. 1 a charge crucible is mounted inposition in the induction coil 23, and the sequencing unit operates theinduction coil supply to initiate its melting cycle. The charge of metalin the crucible is melted in a predetermined fashion so that the entirecharge is melted before a fusible plug at the lower extremity of thecrucible melts to allow the molten metal to flow out. When this occursthe metal flows under gravity through the open gate valve 13 and intomould 33 which is pre-heated to the melting temperature of the metal bythe heating arrangement 32. The amount of metal within the crucible iscarefully arranged to be just sufficient to fill the mould 33. Once themould 33 has been filled, the gate valve 13 is closed by the ram 15,consequently isolating the chamber 10.

The ram 44 is now actuated to retract the plate 45 and consequently towithdraw the mould 33 and chill 34 from the chamber 11. The cam 47regulates the rate of withdrawal such that the mould is quicklywithdrawn from the chamber until a stabilised condition is achievedwhere the heat flow to and from the mould is balanced, the mould is thenslowly withdrawn from the chamber until solidification of the mainportion of the casting is achieved, and finally the mould is quicklywithdrawn completely from the chamber 11 until the cam 47 comes incontact with the micro-switch 50 which halts retraction of the ram 44.In this way optimum properties may be established for different parts ofthe casting.

In this position the mould 33 is fully within the chamber 12, andconsequently the gate valve 14 may be closed by the ram 16, isolatingchamber 11 from chamber 12. The valve 22 is now opened while valve 20 isclosed, thus venting the chambers 10 and 12 to atmosphere while leavingthe chamber 11 evacuated. When the chamber 12 has reached atmosphericpressure the ram 62 operated to lower the spindle 40, whilesimultaneously the ram 31 withdraws the flange 30 and the spent crucible28. When these rams have fully operated the ram 61 rotates the spindle40 so as to bring a new crucible 54 into position above the chamber 10and the new chamber 57 and mould 59 in position below the plate 43.

Once again the ram 62 raises the spindle 40 and brings the chamber 57into sealing engagement with the plate 43, and simultaneously the ram 52lowers the flange 53 into sealing engagement with the top surface of thechamber 10, positioning the crucible 54 within the induction coil 23.

The valve 22 is now closed and the valve 20 opened, evacuating chambersand 57. When this evacuation is complete a pressure sensitive switchcauses rams and 16 to open gate valves 13 and 14, putting chambers 10,11 and 57 into communication with one another. The ram 44 now operatesto raise the spindle 56 and consequently the chill 58 and mould 59 intoposition.

The raising of the mould is again arranged to be at a non-constant ratecalculated to avoid thermal shock damage to the mould while givingoptimum speed of operation.

It should be noted that various modifications to the apparatus describedmay bedesirable. Thus for instance any or all of the chambers 10, 11 and12 may be water cooled either by built-in cooling ducts or bysoldered-on pipes through which cooling water may flow. Again the chargemelting arrangement may differ from that described; for instance atipping crucible may be used to melt and pour the charge.

Furthermore, it may be desirable to alter the mechanisms used to raiseand lower the charging and withdrawal arrangements, for instanceelectrical motors and chain drives rather than hydraulic drives may beused and it may be possible to use a single ram in place of the rams6l'and 62.

We claim:

1. Apparatus for casting comprising first, second and third adjacentchambers each of which may be sealed and evacuated, the chambers beingmounted one above another with the first chamber uppermost, first andsecond valve means dividing said first chamber from said second chamberand said second chamber from said third chamber respectively, a chargemelting arrangement in said first chamber adapted to melt metal anddischarge the molten metal through said first valve means into a mouldsupported within saidsecond chamber during said discharge, a mouldheating furnace in said second chamber adapted to heat said mould, and amovable chill support adapted to carry a chill and said mould betweensaid second and said third chambers wherein said mould is introducedinto said heating furnace and removed when charged from said second tosaid third chamber so that a directional grain structure may be formedin the casting.

2. Apparatus as claimed in claim 1 further compris ing charging meansfor the charge melting arrangement which'comprises a flange memberadapted to carry a crucible which holds the new charge, the firstchamber having an aperture which is sealed by the flange when thecrucible is in positionin the charge melting arrangement.

3. Apparatus as claimed in claim 1 further comprising separate duct meanconnected to said first, second and third chambers for evacuation ofthese chambers.

4. Apparatus as claimed in claim 3 further comprising control meanswhich operate said valves-in sequence so as to maintain at all timesduring the operation a vacuum within the second chamber.

5. Apparatus as claimed in claim 1 further comprising withdrawal meansadapted to withdraw the charged mould from the second chamber at anon-constant predetermined rate.

6. Apparatus as claimed in claim 1 further comprising a single vacuumpumping unit and a single power supply for the bottom pouring equipmentwhich service a plurality of the chamber combinations.

7. Apparatus as claimed in claim 1 further comprising a pair of chargeholding crucibles and flanges and a pair of said third chambers andchill supports, said crucibles and third chambers being movable togetherin a reciprocatory manner between a position in which one of the chargeholding crucibles is located above the first chamber and one of thethird chambers is located below the second chamber and a position inwhich the said one of the charge holding crucibles is remote from thefirst chamber and the said one of the third chambers is remote from thesecond chamber while the other one of the charge holding crucibles andthe other one of the third chambers are positioned adjacent the firstand second chambers respectively.

8. Apparatus as claimed in claim 7 in which the pair of charge holdingcrucibles and the pair of third chambers are mounted on a spindle whichcan be rotated through an are between the said two positions.

9. Apparatus as claimed in claim 7 in which the said third chambers arealternately sealed against the lower surface of the second chamber byupward movement of the third chamber.

1. Apparatus for casting comprising first, second and third adjacentchambers each of which may be sealed and evacuated, the chambers beingmounted one above another with the first chamber uppermost, first andsecond valve means dividing said first chamber from said second chamberand said second chamber frOm said third chamber respectively, a chargemelting arrangement in said first chamber adapted to melt metal anddischarge the molten metal through said first valve means into a mouldsupported within saidsecond chamber during said discharge, a mouldheating furnace in said second chamber adapted to heat said mould, and amovable chill support adapted to carry a chill and said mould betweensaid second and said third chambers wherein said mould is introducedinto said heating furnace and removed when charged from said second tosaid third chamber so that a directional grain structure may be formedin the casting.
 2. Apparatus as claimed in claim 1 further comprisingcharging means for the charge melting arrangement which comprises aflange member adapted to carry a crucible which holds the new charge,the first chamber having an aperture which is sealed by the flange whenthe crucible is in position in the charge melting arrangement. 3.Apparatus as claimed in claim 1 further comprising separate duct meanconnected to said first, second and third chambers for evacuation ofthese chambers.
 4. Apparatus as claimed in claim 3 further comprisingcontrol means which operate said valves in sequence so as to maintain atall times during the operation a vacuum within the second chamber. 5.Apparatus as claimed in claim 1 further comprising withdrawal meansadapted to withdraw the charged mould from the second chamber at anon-constant predetermined rate.
 6. Apparatus as claimed in claim 1further comprising a single vacuum pumping unit and a single powersupply for the bottom pouring equipment which service a plurality of thechamber combinations.
 7. Apparatus as claimed in claim 1 furthercomprising a pair of charge holding crucibles and flanges and a pair ofsaid third chambers and chill supports, said crucibles and thirdchambers being movable together in a reciprocatory manner between aposition in which one of the charge holding crucibles is located abovethe first chamber and one of the third chambers is located below thesecond chamber and a position in which the said one of the chargeholding crucibles is remote from the first chamber and the said one ofthe third chambers is remote from the second chamber while the other oneof the charge holding crucibles and the other one of the third chambersare positioned adjacent the first and second chambers respectively. 8.Apparatus as claimed in claim 7 in which the pair of charge holdingcrucibles and the pair of third chambers are mounted on a spindle whichcan be rotated through an arc between the said two positions. 9.Apparatus as claimed in claim 7 in which the said third chambers arealternately sealed against the lower surface of the second chamber byupward movement of the third chamber.